Plastic housing



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FIS. 3

IN VEN TOR W. R MASQ/V ATTORNEY Patented Jan. 20, 1948 UNITED STATE rms'rro HOUSING Warren P. Mason, yWest Orange, N. J., assignor 'to Bell Telephone Laboratories, Incorporated, i New York, N. Y., a corporation of New York Application May 7, 1943, Serial No. 486,102

This invention relates to housings for electrical apparatus and particularly to housings for electromechanical transducers intended'for operation beneath the surface of the sea.

The object of the invention is to produce a housing for a transducer which will introduce the minimum hindrance to ultrasonic waves traveling inthe sea Water to or from the transducer. Due to the fact thatsuch transducers are immersed to considerable depth in sea water and that the device itselfmust be protected against the sea water, it is usual to place them in a housing and immerse them in anon-corrosive medium such as castor 011,' Heretofore metallic housings have been employed and in some cases small sized windows or diaphragms of material such as very thin steel sheets or fairly thick sheets oi soft rubber have been provided. The metallic housing, however, interferes with the proper transmission of ultrasonic wavesA to and from the transducer and hence it is desirable to employ some other material having the requisite strength but free from the disadvantages of metal.

Applicant has discovered that many plastic materials, transparent and otherwise, possess transmission i. characteristics closely approximating those of sea water. In this connection reference is made to the book Electromechanical trans- ,ducers and Wave lters by this applicant, published in 1942 by D. Van Nostrand Company, Inc., particular reference being made to the chart on page 247 showing the results of` measurements of certain plastics.

A feature of the yinvention is a housing for an electromechanical transducer comprising a 35 plastic structure having transmission characteristics closely approaching those of water.

Other features will appearhereinafter.

The drawings consist of two sheets having four figures, as follows:

Fig. 1 is a view of a housing, partly broken away to show a part of the housing in section and the location of thetransducer;

Fig. 2 is a side view of another form of transducer housing, partly broken away to show the location of the various pieces of apparatus Fig. 3 is a fragmentary sectionaly view of a transducer and its housing of a dierent form; and

Fig. 4 is a perspective view, partly broken away of a streamlined housing.

' In Fig. 1 a mounting plate I is used as a base to support a plurality of crystals 2 comprising an electromechanical transducer. This assembly is `1 claim. (ci. r11-386) quent elimination of the usual losses entailed in the transmission of compressional waves through substances of varying characteristics.

In Fig. 2 a directional projector or hydrophone is shown. In this instance the main body of the housing 5 may be made of any material'but the diaphragm 6 is made of a plastic having the same Y transmission characteristics as the sea water I and the castor oil B. A crystal 9 represents the transducer.

In Fig. 3 there is shown a fragmentary section of a device intended to be placed in a stationary position. A crystal I0 represents a transducer -and this with other apparatus is mounted in a cylindrical shell Il of metal having a plurality of windows cut out. These windows, as well as a layer over the outside of the shell, are formed of ,a plastic I2 which has the same transmission characteristics as the castor oil I3 in which the apparatus is immersed and the sea water I4 which surrounds the assembly.

Fig. 4 shows a streamlined device. The whole is mounted on a shaft I5 bywhich the projector or hydrophone may be lowered or raised or rotated in any desired position, The apparatus I6 represents the transducer which is immersed in castor oil I1 and covered by a housing I8, which as before, is a' plastic of considerable mechanical strength but having practically the same transmission characteristics as the castor oil I1 and the sea water in which the whole is immersed.

The nature of the plastics will be understoodby noting that materials such as polystyrene, various forms of methyl methacrylate, the vinyl chloride acetate resins, cellulose acetate butyrate and certain .of the polyesters may be employed. Of these the cellulose acetate'butyrate and the polyesters give the closest match to. seaI water.

An alternative method which requires a smallerv amount of plastic for the same strength is to mold the plastic around an expanded metal frame somewhat after the fashion Vshown in Fig. 3. The metal frame provides greater mechanical strength, while still allowing free transmission through the large openings in the metal which immersed in a non-corrosive uid 3 such as cas- 66 are nlled with sound transparent Plastics.

What is claimed is: In combination, an electromechanical transducer, non-corrosive liquid having the same impedance characteristics as water in which said transducer is immersed and a. thin wall housing for retaining said liquid, said housing being of a plastic and also having the same impedance characteristics as water.

WARREN P. MASON.

REFERENCES CHTED Number Number UNITED STATES PATENTS Name Date Hoarle Dec. 27. 1938 Hayes Oct. 1, 1935 Hull Apr. 15, 1924 Haines i Feb. 21, 1939 Blake Aug- 3, 1920 FOREIGN PATENTS Country Date Great Britain Feb. 14, 1929 

